An image of the galaxy from the Hubble Space telescope archive, that shows that the underlying galaxy is highly distorted, with extended stellar tails to the left and right. Image: Michael Rauch.
A team of scientists, led by Michael
Rauch from the Carnegie Observatories, has discovered a distant galaxy that may
help elucidate two fundamental questions of galaxy formation: How galaxies take
in matter and how they give off energetic radiation.
During the epoch when the first
galaxies formed, it is believed that they radiated energy, which hit
surrounding neutral hydrogen atoms and excited them to the point where they
were stripped of electrons. This produced the ionized plasma that today fills
the universe. But little is known about how this high-energy light was able to
escape from the immediate surroundings of a galaxy, known as the galactic halo.
The galaxies we observe today tend to be completely surrounded by gaseous halos
of neutral hydrogen, which absorb all light capable of ionizing hydrogen before
it has a chance to escape.
Rauch and his team, using the Magellan
Telescopes at Las Campanas Observatory and archival images from the Hubble
Space Telescope, discovered a galaxy with an extended patch of light
surrounding it. The objects appearance means that roughly half of the galaxy’s
radiation must be escaping and exciting hydrogen atoms outside of its halo.
The key to the escape of radiation can
be found in the unusual, distorted shape of the newly observed galaxy. It
appears that the object had recently been hit by another galaxy, creating a
hole in its halo, allowing radiation to pass through.
“The loss of radiation during galactic
interactions and collisions like the one seen here may be able to account for
the re-ionization of the universe,” Rauch says. “This galaxy is a leftover from
a population of once-numerous dwarf galaxies. And looking back to a time when
the universe was more dense, crashes between galaxies would have been much more
common than today.”
The new observation also helps
scientists better understand the flow of inbound matter, from which a galaxy
originally forms. In the present case, the escaping ionizing radiation
illuminated a long train of incoming gas, which is feeding new matter into the
galaxy. The existence of such structures had been predicted by theory, but they
had not been seen previously because they barely emit any light of their own.